Light guide plate and illumination apparatus

Abstract

A light guide plate includes an extracting light guide layer having a pair of main surfaces. The extracting light guide layer includes a base portion having a pair of main surfaces, and a plurality of light diffusing portions provided in the base portion. The light guide plate can obscure extracting elements for extracting light.

The invention claimed is: 
     
       1. A light guide plate comprising:
 an extracting light guide layer including a base portion having a pair of main surfaces; and 
 light diffusing portions provided in the base portion; 
 wherein two adjacent light diffusing portions, lying next to each other in a first direction, satisfy the following relationship:
   tan(Arcsin( n   L   /n )≦ d /( h   1   +h   2 ),
 
 
 where d is a distance between the two light diffusing portions in the first direction, 
 h 1  and h 2  are heights of the two light diffusing portions in a normal direction of the extracting light guide layer, 
 n is the refractive index of the extracting light guide layer, and 
 n L  is the refractive index of a layer lying adjacent to the extracting light guide layer and superimposed on one of the main surfaces. 
 
     
     
       2. The light guide plate according to  claim 1 ,
 wherein heights of the light diffusing portions in a normal direction of the extracting light guide layer are not equal. 
 
     
     
       3. The light guide plate according to  claim 1 ,
 wherein a height of at least one light diffusing portion in a normal direction of the extracting light guide layer is higher than a height of at least one other light diffusing portion located on one side in a first direction with respect to the one light diffusing portion. 
 
     
     
       4. The light guide plate according to  claim 1 ,
 wherein a height of a light diffusing portion in a normal direction of the extracting light guide layer is not lower than a height of any other light diffusing portion located on one side in a first direction with respect to the light diffusing portion. 
 
     
     
       5. The light guide plate according to  claim 1 , further comprising a low-refractive index layer disposed adjacent to the extracting light guide layer and having a lower refractive index than a refractive index of the base portion of the extracting light guide layer. 
     
     
       6. The light guide plate according to  claim 5 , further comprising a cover layer disposed on the opposite side of the low-refractive index layer from the extracting light guide layer,
 wherein the low-refractive index layer is a layer to bond the extracting light guide layer and the cover layer together. 
 
     
     
       7. The light guide plate according to  claim 6 ,
 wherein the cover layer has higher scratch resistance than a scratch resistance of the base portion of the extracting light guide layer. 
 
     
     
       8. The light guide plate according to  claim 1 ,
 wherein grooves, arranged in the first direction with a space, are formed in one of the pair of main surfaces of the base portion, and 
 wherein the light diffusing portions are provided in the grooves. 
 
     
     
       9. The light guide plate according to  claim 1 ,
 wherein each light diffusing portion extends linearly in a direction not parallel to the first direction. 
 
     
     
       10. An illumination apparatus comprising:
 the light guide plate according to  claim 1 ; and 
 a light source disposed in a position facing a light entrance-side surface of the light guide plate. 
 
     
     
       11. A light guide plate comprising:
 a main light guide layer having a first main surface and a second main surface which oppose each other; 
 a low-refractive index layer provided on the first main surface of the main light guide layer and having a lower refractive index than a refractive index of the main light guide layer; and 
 an extracting light guide layer superimposed on the main light guide layer from a side of the low-refractive index layer, 
 wherein the first main surface includes a first zone and a second zone, and the low-refractive index layer is provided only on the first zone of the first main surface, 
 wherein the extracting light guide layer has extracting elements, arranged in a first direction, for changing the traveling direction of light from the main light guide layer, 
 wherein the extracting elements are provided in a region facing both the first zone and the second zone, 
 wherein the extracting elements are disposed adjacent to the second zone of the main light guide layer, and 
 wherein a difference in refractive index between the extracting elements and the main light guide layer is smaller than a difference in refractive index between the low-refractive index layer and the main light guide layer. 
 
     
     
       12. The light guide plate according to  claim 11 ,
 wherein the extracting light guide layer further has a base portion having a pair of main surfaces, and 
 wherein the extracting elements are light diffusing portions provided in the base portion. 
 
     
     
       13. The light guide plate according to  claim 12 ,
 wherein heights of the extracting elements in a normal direction of the extracting light guide layer are not equal. 
 
     
     
       14. The light guide plate according to  claim 12 ,
 wherein a height of at least one extracting element in a normal direction of the extracting light guide layer is higher than a height of at least one other extracting element located on one side in the first direction with respect to the one light diffusing portion. 
 
     
     
       15. The light guide plate according to  claim 12 ,
 wherein a height of an extracting element in a normal direction of the extracting light guide layer is not lower than a height of any other extracting element located on one side in the first direction with respect to the light diffusing portion. 
 
     
     
       16. The light guide plate according to  claim 12 ,
 wherein grooves, arranged in the first direction with a space, are formed in one of the pair of main surfaces of the extracting light guide layer, and 
 wherein the extracting elements are light diffusing portions formed in the grooves. 
 
     
     
       17. The light guide plate according to  claim 11 ,
 wherein each extracting element extends linearly in a direction not parallel to the first direction. 
 
     
     
       18. An illumination apparatus comprising:
 the light guide plate according to  claim 11 ; and 
 a light source disposed in a position facing a light entrance-side surface of the light guide plate.